Hydrogenolysis/dehydrohalogenation process

ABSTRACT

A process for the hydrogenolysis and/or dehydrohalogenation of fluorohalocarbons and/or fluorohalohydrocarbons by reacting the fluorohalocarbons and/or fluorohalohydrocarbons with a source of hydrogen in the presence of a catalyst, the improvement comprising utilizing a rhenium-containing catalyst, which may, optionally, contain at least one Group VIII metal and may, optionally, be supported.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of pending U.S. patent application Ser.No. 07/596,551, filed Oct. 17, 1990, now U.S. Pat. No. 5,068,473, whichis a continuation of U.S. patent application Ser. No. 07/305,698, filedFeb. 3, 1989, and abandoned.

FIELD OF THE INVENTION

Improved process for the hydrogenolysis and/or dehydrohalogenation offluorohalocarbons and/or fluorohalohydrocarbons utilizing a rheniumcatalyst.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 2,615,925 claims a process for producing a fluoroolefin bypassing a mixture containing a chlorofluoro-compound over a metalliccopper catalyst at 460° to 700° C. In an example1,1,1,2-tetrachloro-2,2-difluoroethane and hydrogen were passed over acopper catalyst at 370° C. to 390° C. to obtain a 72% yield of1,1-dichloro-2,2-difluoroethylene.

GB 698,386 discloses a process for making CClF═CF₂ by passing a mixtureof CCl₂ FCClF₂ (CFC-113) and hydrogen through an empty reactor at 450°to 650° C., or for higher efficiency through a reactor charged with acatalyst containing nickel, copper, cobalt, platinum, or palladium,either supported on carbon or unsupported, at 375° to 525° C. CClF=CF₂was produced in 52% yield while the major byproduct, CF₂ ═CHF wasproduced in 5% yield.

U.S. Pat. No. 2,942,036 discloses a process for the reaction of CF₃ CCl₂CClF₂ (CFC-215aa) with hydrogen over a palladium/carbon catalyst at175°-350° C. to recover a product stream containing about 10% CF₃CCl═CF₂, about 15-16% CF₃ CH═CF₂, about 60% CF₃ CH₂ CHF₂, and about 6-7%unreacted CFC-215aa.

U.S. Pat. No. 3,043,889 discloses a process for making CClF═CF₂ fromCFC-113 and hydrogen by passing the mixture over a chromium oxidecatalyst at 475°-550° C. Per pass conversions of CFC-113 of 15-30% wereobserved (col. 6, lines 17-30).

CA 655,397 claims a process for making CHF═CF₂ in larger amounts thanCH₂ FCHF₂ from CFC-113 by passing a mixture of hydrogen and CFC-113 overa Pd/C catalyst. The production of CClF═CF₂ is inhibited by adjustingthe mol ratio of H₂ /CFC-113 to be in the range of 0.7-1.7. In a typicalexample, CFC-113 and hydrogen at 265° C. are passed over a 1% Pd/Ccatalyst to obtain a 38% conversion to CHF═CF₂ and a 25% conversion toCH₂ FCHF₂.

U.S. Pat. No. 3,505,417 discloses a process for the dehydrohalogenationof fluorohalocarbons using hydrogen over a catalytic compositionconsisting essentially of aluminum fluoride and at least one metallicelement selected from groups I through VIII of the periodic table. Thecatalysts can also contain at least one metallic element which does notadversely affect their activity; some examples of which include:magnesium, barium, copper, sodium, potassium, chromium, nickel,molybdenum, vanadium, zinc, tin, silver, tungsten, iron, indium,titanium, germanium, platinum, palladium, rhodium, rhenium, osmium, andiridium. The patent claims a process for the dehydrohalogenation offluorohalocarbons in the presence of hydrogen and a catalyticcomposition consisting of aluminum fluoride and from 0.05-30 weightpercent of at least one of CuO, Cr₂ O₃, RhCl₃, Co0, and Pt at 200°-600°C. When 1,2-dichloro-1,1,2,2-tetrafluoroethane (CFC-114) and hydrogenwere passed over a copper oxide-cobalt oxide on fluorinated aluminacatalyst, a 95% conversion of CFC-114 with a 78% yield oftetrafluoroethylene was obtained (Example 2).

U.S. Pat. No. 3,636,173 discloses a process and catalysts for thedehydrohalogenation of fluorohalocarbons using hydrogen and a catalyticcomposition containing aluminum fluoride and preferably a Group I-B,II-B, VI-B or Group VIII metal phosphate. Catalysts containing nickel orchromium phosphate are especially preferred. When CFC-113 and hydrogenwere passed over a nickel phosphate catalyst at 385° C, a 98% conversionof CFC-113 with a 54% yield of chlorotrifluoroethylene was obtained(col. 5, lines 40-48).

GB 1,578,933 discloses a process for the manufacture of CF₃ CH₂ F(HCF-134a) or CHF₂ CHF₂ (HFC-134) by the hydrogenolysis of anappropriate haloethane over a hydrogenation catalyst. Palladiumsupported on carbon or alumina are specifically claimed. In Ex. 3 a 94%conversion of CF₃ CFCl₂ (CFC-114a) with a 76% selectivity to HFC-134aand a 6.5% selectivity to CF₃ CFHCl (HCFC-124)/CF₂ HCF₂ Cl (HCFC-124a)for the hydrogenolysis of CFC-114a over a Pd/C catalyst at 310° C. isdescribed.

C. Gervasutti et. al., J. Fluorine Chem., 19, 1 (1981) disclose thepreparation of HFC-134a from the selective hydrogenolysis of isomericmixtures of dichlorotetrafluoroethanes catalyzed by Pd/C to HFC-134a,CF₃ CH₃ (HFC-143a) and HCFC-124 with a selectivity of 77.8%, 12.6% and9.7% respectively.

U.S. Pat. No. 4,319,060 discloses a process for producing CF₂ ClCF₂ Cl(CFC-114) substantially free of CFC-114a by the selective hydrogenolysisof a feed stream containing 0.1 to 25 weight percent of CFC-114a and 75up to less than 100 weight percent of CFC-114 over a supported preciousmetal catalyst at 100°-300° C.

EP 164,954 discloses a method for the preparation of CF₃ CHFCl(HCFC-124) from CF₃ CFCl₂ (CFC-114a) using an alkali metal amalgam in anactive hydrogen containing (e. g., an alcohol) liquid medium.

The art shows that numerous catalysts, some of which are describedabove, for the hydrogenolysis and/or dehydrohalogenation offluorohalocarbons are known. From the selectivities achieved in the artcited above, it is clear that there is a need for more selectivecatalysts. This need is particularly great because the products of thesereactions are useful as environmentally desirable compounds for use assolvents, blowing agents and, particularly, refrigerants.

An object of this invention is to provide a process having improvedselectivity and high conversion to the desired products.

SUMMARY OF THE INVENTION

This invention provides for an improvement in the process for thehydrogenolysis and/or dehydrohalogenation of fluorohalocarbons and/orfluorohalohydrocarbons by reacting the fluorohalocarbons and/orfluorohalohydrocarbons with a source of hydrogen in the presence of acatalyst. The improvement comprises utilizing a rhenium-containingcatalyst.

The products of the improved hydrogenolysis and/or dehydrohalogenationcan be obtained with combined selectivities of at least 90%. Inaddition, the rhenium-containing catalyst used in the practice of thisinvention is lower in cost than conventionally used noble metalcatalysts and may also be more resistant to catalyst poisoning.

DETAILS OF THE INVENTION

The rhenium-containing catalyst useful in the practice of this inventionmay, optionally, contain a minor proportion of metals from Group VIII ofthe periodic table, e.g., Pt, Pd, Ru or Rh. The rhenium-containingcatalyst may, or may not be supported. When not supported and combinedwith other metals, the amount of rhenium is at least 50% by weight, thebalance being at least one selected from Group VIII metals.

The rhenium-containing material used to prepare the catalyst may beselected from rhenium metal; an organometallic rhenium compound, e.g.cyclopentadienylrhenium tricarbonyl; perrhenic acid; rhenium carbonyl;rhenium (III or IV) or chloride, or rhenium (IV, VI, or VII) oxide. Theother metals, which may be added to the catalysts are those from GroupVIII, e.g. Pt, Pd, Ru or Rh. The metal may be added in any form known tothe art e.g., as a soluble salt of the metal.

The rhenium-containing catalyst may be supported on carbon, alumina,fluorided alumina, aluminum fluoride, calcium fluoride, or othersupports, with carbon being the most preferable. The fluorided aluminacan be prepared from either aluminum chloride or alumina by treatmentwith HF or a fluorine containing compound as is well known in the art.Alumina containing rhenium and, optionally, Group VIII metals may alsobe fluorided by treatment with HF or a fluorine-containing compound toproduce the rhenium-containing catalyst. The alumnium chloride derivedsupport may be an aluminum chlorofluoride, while the alumina derivedsupport may contain oxyfluorides, hydroxyfluorides, and unreactedalumina.

The supported catalysts of the instant invention can be prepared byimpregnating the support material with a solution of therhenium-containing material and also, optionally, with solutions ofGroup VIII-containing materials. The concentration of rhenium on thesupport can range from 0.1% to 20% by weight. The concentration of GroupVIII metals on the support can range from 0% to 10% by weight, butrhenium is always the major component.

The invention is applicable to the hydrogenolysis and/ordehydrohalogenation of fluorohalocarbons and/or fluorohalohydrocarbonsthat contain one or more fluorine atoms in the molecule. Thefluorohalocarbons and/or fluorohalohydrocarbons are preferably thosewherein halo is chloro or bromo. Included are fluorohalocarbons andfluorohalohydrocarbons composed, respectively of: carbon, chlorine,and/or bromine and fluorine; and carbon, hydrogen, chlorine and/orbromine and fluorine. The fluorohalocarbons and/orfluorohalohydrocarbons may contain 1 to 10 carbon atoms, preferably 1 to4 carbon atoms. The fluorohalocarbons and/or fluorohalohydrocarbonsinclude cyclic as well as acyclic compounds represented by the empiricalformula C_(n) H_(m) F_(p) X_(q), where X is Cl and/or Br, preferably Cl,and n is an integer from 1 to 10, m is an integer from 0 to 20, p is aninteger from 1 to 21, and q is an integer from 1 to 21, provided thatm+p+q=2n+2 when the compound is acyclic and equals 2n when the compoundis cyclic.

In a preferred embodiment the fluorohalocarbons and/orfluorohalohydrocarbons are represented by the above empirical formulawhere n=1 to 4, m is 0 to 8, p is 1 to 9, and q is 1 to 9.

The fluorohalocarbons and/or fluorohalohydrocarbons also includearomatic compounds represented by the formula, C₆ H_(n) F_(p) X_(q),where X is Cl and/or Br, preferably Cl, and n is an integer from 0 to 4,p is an integer from 1 to 5, and q is an integer from 1 to 5, providedthat n+p+q=6 and that when p=5, n=0; or by the formula C₅ NH_(n) F_(p)X_(q), where X is Cl and/or Br, preferably Cl, and n is an integer from0 to 3, p is an integer from 1 to 4, and q is an integer from 1 to 4,provided that n+p+q=5 and that when p=4, n=0.

The products of the hydrogenolysis and/or dehydrohalogenation reactionsof the C₁ fluorohalocarbons or fluorohalohydrocarbons may contain one totwo hydrogen atoms and those from C₂ compounds from one to threehydrogen atoms with those containing one for the one carbon species andtwo to three for the two carbon species being preferred. The C₃fluorohalocarbons or fluorohalohydrocarbons hydrogenolysis products maycontain one to five hydrogen atoms with those containing one or fourbeing preferred. In a similar manner the C₄ to C₁₀ hydrogenolysisproducts may contain one or more hydrogen atoms. It is to be understoodthat some or all of the reaction products from C₂ to C₁₀ may containsaturated or unsaturated carbon-carbon bonds.

A particularly desirable feature of utilizing the rhenium-containingcatalyst in accordance with this invention is that the products of thehydrogenolysis and/or dehydrohalogenation will contain in highselectivity just one less chlorine than was present in the startingmaterial.

The reaction temperature can range from about 100° C. to about 400° C. Apreferred range is about 150° C. to about 350° C.

The amount of hydrogen contained in the gas stream contacted with thegaseous fluorohalocarbon and/or fluorohalohydrocarbon should be at least0.2 moles per mole of fluorohalocarbon and/or fluorohalohydrocarbon andpreferably from 0.5 to 5 moles.

Hydrogen can be fed either in the pure state or diluted with an inertgas, e.g., nitrogen, helium, or argon.

While vapor phase reactions are preferred, the catalysts may also beused for liquid phase hydrogenolysis reactions.

The products, consisting of either pure fluorohalocarbons orfluorohalohydrocarbons or mixtures of fluorohalocarbons andfluorohalohydrocarbons and a hydrogen halide, can be separated andpurified by conventional means such as distillation.

A key feature of this invention is that through catalyst selection and,optionally, process control, such as variation of H₂ /organic ratios,space velocity, pressure and temperature, a desired fluorocarbon may beobtained as a major product with high selectivity and minimal formationof unwanted by-products.

The fluorohalocarbons and/or fluorohalohydrocarbons utilized in theprocess of this invention are either commercially available or can beprepared by known methods.

The hydrogenolysis reactions may be conducted in any suitable reactor,including fixed and fluidized bed reactors. The reaction vessel shouldbe constructed of materials which are resistant to the corrosive effectsof hydrogen halide such as Hastelloy® alloy or Inconel® alloy.

Pressure is not critical. Atmospheric pressure is preferred fordehydrohalogenation and atmospheric or superatmospheric pressures forhydrogenolysis.

The products of these reactions may be used as solvents, blowing agents,refrigerants, propellants, and polymer intermediates.

EXAMPLES

All parts and percentages are by weight and all temperatures are degreesCelsius, unless otherwise noted. The following examples serve toillustrate the invention but they are not intended to limit it thereto.

General Procedure

A designated quantity of catalyst was charged to a 1 cm diameter x 10 cmlength Vycor® reactor, which was heated in a tube furnace. Hydrogen anda fluorohalocarbon or a fluorohalohydrocarbon vapor, or liquidfluorohalocarbon or fluorohalohydrocarbon which was vaporized in apreheated zone, were passed over the catalyst at the designatedtemperatures, flow rates, and at atmospheric pressure except forExamples 1, 4, 10, and 11, which were done at 740, 846, 155, and 155 kParespectively. The reactor effluent was passed directly into a gaschromatograph equipped with a flame-ionization detector. Examples, 1, 3,4, 10, and 11 were conducted in a 316 stainless steel reactor placed ina fluidized sand bath. The catalyst was loaded into the reactor andpurged with N₂ followed by a H₂ purge. The temperature was thenincreased from room temperature to 300° or 350° C. at 0.5° C./min, heldat maximum temperature, under hydrogen, for two hours, followed bycooling to the desired temperature for the reaction. The reactoreffluent was analyzed as above. All percentages are area percent exceptExamples 1, 4, 10, and 11, where they are mol percent.

A 5% Re/C catalyst was prepared by adding calcined carbon granules (50g, 20-50 mesh) to a rhenium heptoxide solution (33 mL of a 0.2 molarsolution) which was further diluted with distilled water (52 mL). Thegranules were stirred occasionally and kept at room temperature forthree hours. They were then dried at 110° C. in air for 18 hoursfollowed by one hour at 150° C. in helium (100 cc/min), and one hourwith a 1/1 He/H₂ mixture (200 cc/min). The temperature was then raisedto 300° C. while passing the He/H₂ mixture over it and maintained for 3hours. Finally the catalyst was cooled to room temperature andpassivated with 1.5% oxygen in nitrogen for 18 hours.

EXAMPLE 1 1,1,1-Trichloro-2,2,2-trifluoroethane (CFC-113a)Hydrogenolysis

The catalyst was 5% Re/C (1.2 g) and the flow rates of H₂ and CFC-113awere 7.6 cc/min and 2 mL/h respectively and the reactor temperature was202° C. After 59 hours of operation, CFC-113a conversion was 20% andselectivity to CF₃ CHCl₂ was 96%.

The Re/C catalyst as used herein is preferred for hydrogenolysis ofCFC-113a, because when a Re/Alumina catalyst was utilized under similarreaction conditions, a significant quantity of CF₃ CCl═CClCF₃ wasproduced at the expense of the desired CF₃ CHCl₂.

COMPARATIVE EXAMPLE A 1,1,1-Trichloro-2,2,2-trifluoroethane (CFC-113a)Hydrogenolysis

The catalyst was 0.5% Pd/C (1.2 g) and the flow rates of H₂ and CFC-113awere 7.6 cc/min and 2 mL/h, respectively. The reaction temperature was118° C. The following results were obtained by gas chromatographicanalysis; 48% conversion of CFC-113a with the following selectivities,10% CF₃ CHCl₂, 1% CF₃ CH₂ Cl and 33% CF₃ CH₃. The rhenium based catalystis seen to be far more selective for the removal of only one chlorineatom.

EXAMPLE 2 1,1,2-Trichloro-1,2,2-trifluoroethane (CFC-113) Hydrogenolysis

The catalyst was 5% Re/Al₂ O₃ (2.0 g) and the flow rates of H₂ andCFC-113 were 10 cc/min and 1 mL/h respectively. Hydrogenolysis resultsare shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Run  Temp.    CF.sub.2 ClCFCl.sub.2                                                                    CF.sub.2 ClCFHCl                                                                         FClC═CF.sub.2                         No.  °C.                                                                             % Conv.    % Sel.     % Sel.                                    ______________________________________                                        1    210       5         50         50                                        2    282      30         71         29                                        3    325      78         78         15                                        ______________________________________                                    

EXAMPLE 3 CFC-113 Dehydrohalogenation

The catalyst was 5% Re/C (2.6 g) and the flow rates of H₂ and CFC-113were 6 cc/min and 2 mL/h respectively. Dehydrohalogenation results areshown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Run  Temp.    CF.sub.2 ClCFCl.sub.2                                                                    CF.sub.2 ClCFHCl                                                                         ClFC═CF.sub.2                         No.  °C.                                                                             % Conv.    % Sel.     % Sel.                                    ______________________________________                                        1    200      15          5         95                                        2    250      91         20         80                                        3    300      78         11         85                                        ______________________________________                                    

EXAMPLE 4 1,1-Dichloro-1,2,2,2-tetrafluoroethane (CFC-114a)Hydrogenolysis

The catalyst was 5% Re/C (1.2 g) and the flow rates of H₂ and CFC-114awere 7.6 cc/min and 1 mL/h respectively, and the reactor temperature was253° C. Hydrogenolysis results are shown in Table 3.

                                      TABLE 3                                     __________________________________________________________________________    Run                                                                           Time                                                                             Temp.                                                                              CH.sub.3 CFCl.sub.2                                                                 CF.sub.3 CFHCl                                                                       CF.sub.3 CH.sub.2 F                                                                 CF.sub.3 CH.sub.3                                                                   Other.sup.1                                  Hrs.                                                                             °C.                                                                         % Conv.                                                                             % Sel. % Sel.                                                                              % Sel.                                                                              % Sel.                                       __________________________________________________________________________    10.6                                                                             253  61    81     0.5   1     16                                           18.3                                                                             253  54    82     0.5   1     15                                           __________________________________________________________________________     .sup.1 The major components are CF.sub.3 CH═CHCF.sub.3 and                FClC═CF.sub.2.                                                       

EXAMPLE 5 CFC-114a Hydrogenolysis

The catalyst was 1% Pd/4% Re/C (0.2 g) and the flow rates of H₂ andCFC-114a were 11 cc/min and 5 cc/min respectively. Hydrogenolysisresults are shown in Table 4.

COMPARATIVE EXAMPLE B 1,1-Dichloro-1,2,2,2-tetrafluoroethane (CFC-114a)Hydrogenolysis

The catalyst was 0.5% Pd/C (0.2 g) and the flow rates of H₂ and CFC-114awere 12.5 cc/min respectively. The reaction temperature was 225° C. Thefollowing results were obtained by gas chromatographic analysis; 67%conversion of CFC-114a with the following selectivities, 14% CF₃ CFHCl,78% CF₃ CH₂ F and 7% CF₃ CH₃. The rhenium based catalyst is seen to befar more selective for the removal of only one chlorine atom.

                  TABLE 4                                                         ______________________________________                                        Run   Temp.   CF.sub.3 CFCl.sub.2                                                                     CF.sub.3 CFHCl                                                                        CF.sub.3 CH.sub.2 F                                                                   CF.sub.3 CH.sub.3                     No.   °C.                                                                            % Conv.   % Sel.  % Sel.  % Sel.                                ______________________________________                                        1     197     46        77      16       7                                    2     216     69        77      16       7                                    3     242     88        74      17       9                                    4     266     95        67      17      11                                    5     297     98        54      21      16                                    6     327     98        35      28      25                                    ______________________________________                                    

EXAMPLE 6 1,2-Dichloro-2,2,2-trifluorethane (HCFC-123) Hydrogenolysis

The catalyst was 5% Re/C (2 g) and the flow rates of H₂ and HCFC-123were 11 cc/min and 1 mL/h respectively. Hydrogenolysis results are shownin Table 5.

                  TABLE 5                                                         ______________________________________                                        Run     Temp.   CF.sub.3 CHCl.sub.2                                                                       CF.sub.3 CH.sub.2 Cl                                                                  CF.sub.3 CH.sub.3                         No.     °C.                                                                            % Conv.     % Sel.  % Sel.                                    ______________________________________                                        1       211     44          91      1                                         2       240     87          90      5                                         3       254     99          92      5                                         ______________________________________                                    

EXAMPLE 7 Chloro-1,2,2,2-tetrafluoroethane (HCFC-124) Hydrogenolysis

The catalyst was 5% Re/C (1 g) and the flow rates of H₂ and HCFC-124were 6 cc/min and 5 cc/min respectively. Hydrogenolysis results areshown in Table 6.

                  TABLE 6                                                         ______________________________________                                        Run     Temp.   CF.sub.3 CHFCl                                                                            CF.sub.3 CH.sub.2 F                                                                   CF.sub.3 CH.sub.3                         No.     °C.                                                                            % Conv.     % Sel.  % Sel.                                    ______________________________________                                        1       280      9          53      44                                        2       321     24          40      54                                        3       360     48          31      62                                        ______________________________________                                    

EXAMPLE 8 1,1,1,3,3,3-Hexafluoro-2,2-dichloropropane (CFC-216aa)Hydrogenolysis

The catalyst was 5% Re/Al₂ O₃ (2.0 g) and the flow rates of H₂ andCFC-216aa were 5 cc/min and 1 mL/h respectively. Hydrogenolysis resultsare shown in Table 7.

                  TABLE 7                                                         ______________________________________                                        Run   Temp.   CF.sub.3 CCl.sub.2 CF.sub.3                                                              CF.sub.3 CHClCF.sub.3                                                                   CF.sub.3 CCl═CF.sub.2                  No.   °C.                                                                            % Conv.    % Sel.    % Sel.                                     ______________________________________                                        1     210     80         91        9                                          2     247     90         85        15                                         3     289     96         94        2                                          ______________________________________                                    

EXAMPLE 9 CFC-216aa Hydrogenolysis

The catalyst was 5% Re/C (1.0 g) and the flow rates of H₂ and CFC-216aawere 6.5 cc/min and 1 mL/h respectively. Hydrogenolysis results areshown in Table 8.

                  TABLE 8                                                         ______________________________________                                        Run Temp. CF.sub.3 CCl.sub.2 CF.sub.3 CF.sub.3 CHClCF.sub.3 CF.sub.3          CH.sub.2 CF.sub.3                                                             CF.sub.3 CCl═CF.sub.2 CF.sub.3 CH═CF.sub.2                            No.  °C.                                                                           % Conv.   % Sel. % Sel. % Sel. % Sel.                             ______________________________________                                        1    177    28        68     --     32     --                                 2    216    64        73     0.1    27     0.9                                3    245    100       63     2      25     10                                 ______________________________________                                    

EXAMPLE 10 1,2-Dichloro-2,2-difluoroethane (HCFC-132b) hydrohalogenation

The catalyst was 5% Re/C (40.4 g) and the flow rates of H₂ and HCFC-132bwere 30 cc/min and 3 mL/h. The reaction was carried out at 278° C. and155 kPa. The reaction product stream, after a run of 53 hours, containedthe following compounds (mol %); 71% CF₂ ═CH₂, 0.4% CH₂ ═CH₂, 0.1% CF₃CH₃, 0.4% CF₂ HCH₃, 15% CF₂ ClCH₃, 0.5% CF₂ ═CHCl, 0.1% CHF₂ CHFCl, and12% CF₂ ClCH₂ Cl. The yield of CF₂ ═CH₂ (based on HCFC-132b converted)was 80%.

EXAMPLE 11 HCFC-132b Dehydrohalogenation

The catalyst was 5% Re/C (2.64 g) and the flow rates of H₂ and HCFC-132bwere 5 cc/min and 2 mL/h. The reaction was carried out at 350° C. and155 kPa. The reaction product stream contained 35% CF₂ ═CH₂ and 64%HCFC-132b. The reacton was repeated using 2× the hydrogen (10 cc/min)and the following was found in the product stream; 27% CF₂ ═CH₂ and 72%HCFC-132b. The temperature was lowered to 300° C. and the reactionrepeated using the last set of conditions and a product streamcontaining 21% CF₂ ═CH₂ and 78% HCFC-132b was found.

EXAMPLE 12 1,2-Dichloro-1,2,3,3,4,4-hexafluorocyclobutane (C-316)Dehydrohalogenation

The catalyst was 5% Re/C (1.0 g) and the flow rates of H₂ and C-316 were20 cc/min and 1 mL/h respectively. The reaction was done at 300° C andthe products were analyzed by gas chromatography. All the startingmaterial was consumed and only one peak was detected, which by NMRanalysis was shown to be perfluorocyclobutene produced with 100%selectivity.

EXAMPLE 13 Bromopentafluorobenzene Hydrogenolysis

The catalyst was 5% Re/C (1.0 g) and the flow rates of H₂ andbromopentafluorobenzene were 5 cc/min and 1 mL/h respectively. Afterreaction at 300° C., the products were analyzed by 19F-NMR andpentafluorobenzne was found with a selectivity of 87%.

EXAMPLE 14 2,4,6-Trifluoro-3,5-dichloropyridine Hydrogenolysis

The catalyst was 5% Re/C (1.0 g) and the flow rates of H₂ and a solutionof 2,4,6-trifluoro-3,5-dichloropyridine in hexafluorobenzene were 10cc/min and 1 mL/h respectively. After reaction at 300° C., analysis by¹⁹ F-NMR of the product stream showed a 60% conversion of the startingmaterial to 2,4,6-trifluoro-3-chloropyridine with a selectivity of 93%.

What is claimed:
 1. In a process for the dehydrohalogenation offluorohalohydrocarbons which contain at least one halo group selectedfrom chloro and bromo by reacting the fluorohalohydrocarbons with asource of hydrogen in the presence of a catalyst, the improvementcomprising utilizing a rhenium-containing catalyst selected form thegroup consisting of (i) catalysts consisting essentially of rhenium,(ii) unsupported catalysts containing at least about 50 percent byweight rhenium with the balance being one or more Group VIII metals,(iii) catalysts consisting essentially of rhenium supported on carbon orcalcium fluoride, and (iv) supported catalysts consisting essentially ofone or more Group VIII metals and from 0.1 to 20 percent by weight ofrhenium supported on carbon or calcium fluoride, wherein said one ormore Group VIII metals total up to 10 percent by weight and rhenium isthe major component on said support.
 2. The process of claim 1 whereinthe rhenium-containing catalyst consists essentially of rhenium.
 3. Theprocess of claim 1 wherein the rhenium-containing catalyst consistsessentially of at least 50% by weight of rhenium, the balance beingselected from at least one Group VIII metal.
 4. The process of claim 1or 2 wherein the rhenium-containing catalyst is supported on carbonand/or calcium fluoride.
 5. The process of claim 1 wherein thedehydrohalogenation is conducted at a temperature from about 100° C. toabout 400° C.
 6. The process of claim 1 wherein the source of hydrogenis present in an amount of at least 0.2 moles per mole offluorohalohydrocarbons.
 7. The process of claim 1 wherein thefluorohalohydrocarbons are selected from at least one of cyclic andacyclic compounds represented by the empirical formula C_(n) H_(m) F_(p)X_(q), where X is Cl and/or Br; n is an integer from 2 to 10; m is aninteger from 1 to 20; p is an integer from 1 to 21; and q is an integerfrom 1 to 21, provided that m+p+q=2n+2 when the compound is acyclic andequals 2n when the compound is cyclic.
 8. The process of claim 1 wherein1,1-dichloro-2,2-difluoroethane is dehydrohalogenated.
 9. The process ofclaim 1 wherein 1,2-dichloro-1,2,3,3,4,4-hexafluorocyclopentane isdehydrohalogenated.
 10. In a process for the combined hydrogenolysis anddehydrohalogenation of fluorohalocarbons which contain halogensubstituents selected from the group consisting of chlorine and bromineby reacting the fluorohalocarbons with a source of hydrogen in thepresence of a catalyst, the improvement comprising utilizing arhenium-containing catalyst selected from the group consisting of (i)catalysts consisting essentially of rhenium, (ii) unsupported catalystscontaining at least about 50 percent by weight rhenium with the balancebeing one or more Group VIII metals, (iii) catalysts consistingessentially of rhenium supported on carbon or calcium fluoride, and (iv)supported catalysts consisting essentially of one or more Group VIIImetals and from 0.1 to 20 percent by weight of rhenium supported oncarbon or calcium fluoride, wherein said one or more Group VIII metalstotal up to 10 percent by weight and rhenium is the major component onsaid support.
 11. The process of claim 10 wherein the rhenium-containingcatalyst consists essentially of rhenium.
 12. The process of claim 10wherein the rhenium-containing catalyst consists essentially of at least50% by weight of rhenium, the balance being selected from at least oneGroup VIII metal.
 13. The process of claim 10 or 11 wherein therhenium-containing catalyst is supported on carbon and/or calciumfluoride.
 14. The process of claim 10 wherein the combinedhydrogenolysis and dehydrohalogenation is conducted at a temperaturefrom about 100° C. to about 400° C.
 15. The process of claim 10 whereinthe source of hydrogen is present in an amount of at last 0.2 moles permole of fluorohalocarbons.
 16. The process of claim 10 wherein thefluorohalocarbons are selected from at least one of cyclic and acycliccompounds represented by the empirical formula C_(n) F_(p) X_(q), whereX is Cl and/or Br; n is an integer from 2 to 10; p is an integer from 1to 21; and q is an integer from 2 to 21, provided that m+p+q=2n+2 whenthe compound is acyclic and equals 2n when the compound is cyclic. 17.The process of claim 10 wherein chlorotrifluoroethylene is formed from1,1,2-trichloro-1,2,2-trifluoroethane.